In thermally highly stressed turbines, the turbine blades are provided on the outside with a normally ceramic protective layer. Examples of such protective layers can be gathered from EP 2 085 498 A1. With the aid of such protective layers, the turbine can be operated at higher temperatures and, in this way, the efficiency thereof can be improved. In addition, such turbine blades have cooling air holes via which cooling air, which is supplied to the cooling air holes from inside via cooling air ducts, can emerge.
The protective layers of such turbine blades are subject to wear. The protective layer must therefore be renewed from time to time. The residues of the remaining protective layer must be removed first, before the new protective layer is applied. During the process, the cooling air holes are partly or completely closed by the material of the new protective layer.
In the prior art, the opening of the cooling air holes is still done by hand with the aid of a file, the cooling air holes being identified by using slight depressions in the protective layer or small non-central holes. This process is time-consuming and therefore costly.